The detection of aerosols within fluid samples can be accomplished by optical methods. Such methods are useful in detecting potentially harmful aerosols, such as biological aerosols that may be present after a biological agent attack or industrial accident. It is well known that biological molecules fluoresce when excited by ultraviolet (UV) radiation. As a result, biological molecules in an aerosol sample can be optically detected by irradiating the sample with ultraviolet radiation, and observing the fluorescence response. Since differing excitation wavelengths may be used to detect different classes of biological molecules, the excitation wavelength can be chosen to detect specific classes of biological molecules such as proteins, flavinoids, and metabolite products.
A biological aerosol detector of the type described above is described in more detail in U.S. patent application Ser. No. 10/720,877, now allowed, which is incorporated herein by reference. The detector described in patent application Ser. No. 10/720,877, includes a light source 4, which can be a UV laser light source or an LED light source. Recently, UV light sources in the form of semiconductor ultraviolet optical sources or SUVOS have become available. These light sources typically have both a primary emission band with a center wavelength in the ultraviolet region (i.e., a primary emission band that is capable of eliciting a fluorescence response from a biological aerosol), and a secondary emission tail at longer wavelengths that overlaps and interferes with the fluorescence response. When SUVOS type light sources are used in the biological aerosol detector described in patent application Ser. No. 10/720,877, light from the source's secondary emission band can be scattered by particles in the aerosol detector's optical cavity, thereby creating a positive response signal in the aerosol detector regardless of whether the scattering particle was a biological molecule or not. To reduce the occurrence of these types of false positive signals, the radiation from the SUVOS's secondary emission band must be attenuated to prevent it from entering the aerosol detector's optical cavity.